This invention relates to an electronic musical instrument of a type having a filtering function wherein the slope of a filter can continuously be changed.
In general natural musical instruments such as, for example, wind instruments, piano, etc., a spectrum envelope of a musical tone which determines its tone color changes dependent upon an emphasis placed on performance or upon in advancement of attenuation. For example, in case of a wind instrument such as a trumpet, when it is played with a small volume, the slope of the level of frequency components is steep in a higher frequency range whereas when it is played with a large volume, the slope is gradual in the higher frequency range, i.e., the inclination of the slope tends to become more gradual as the volume increases. In the case of a piano, the slope becomes steep as the attenuation of the tone is advanced. The steep slope in the spectrum envelope means that the amount of attenuation is large in harmonic components of higher orders in the spectrum envelope determining a tone color, i.e., an effective level of these harmonic components is low and number of harmonics contained in the spectrum envelope tends to be decreased. On the other hand, a gradual slope means the reverse to the above. Such variations in the spectrum envelope are accepted as natural to a human sense.